.\" RCSid "$Id: rpict.1,v 1.23 2018/03/20 02:40:38 greg Exp $"
.TH RPICT 1 2/26/99 RADIANCE
.SH NAME
rpict - generate a RADIANCE picture
.SH SYNOPSIS
.B rpict
[
.B options
]
[
.B $EVAR
]
[
.B @file
]
[
.B octree
]
.br
.B "rpict [ options ] \-defaults"
.SH DESCRIPTION
.I Rpict
generates a picture from the RADIANCE scene given in
.I octree
and sends it to the standard output.
If no
.I octree
is given, the standard input is read.
(The octree may also be specified as the output of a command
enclosed in quotes and preceded by a `!'.)\0
Options specify the viewing parameters as well as
giving some control over the calculation.
Options may be given on the command line and/or read from the
environment and/or read from a file.
A command argument beginning with a dollar sign ('$') is immediately
replaced by the contents of the given environment variable.
A command argument beginning with an at sign ('@') is immediately
replaced by the contents of the given file.
.PP
In the second form shown above, the default values
for the options (modified by those options present)
are printed with a brief explanation.
.PP
Most options are followed by one or more arguments, which must be
separated from the option and each other by white space.
The exceptions to this rule are the 
.I \-vt
option and the boolean options.
Normally, the appearance of a boolean option causes a feature to
be "toggled", that is switched from off to on or on to off
depending on its previous state.
Boolean options may also be set
explicitly by following them immediately with a '+' or '-', meaning
on or off, respectively.
Synonyms for '+' are any of the characters "yYtT1", and synonyms
for '-' are any of the characters "nNfF0".
All other characters will generate an error.
.TP 10n
.BI -vt t
Set view type to
.I t.
If
.I t
is 'v', a perspective view is selected.
If
.I t
is 'l', a parallel view is used.
A cylindrical panorma may be selected by setting
.I t
to the letter 'c'.
This view is like a standard perspective vertically, but projected
on a cylinder horizontally (like a soupcan's-eye view).
Three fisheye views are provided as well; 'h' yields a hemispherical fisheye
view, 'a' results in angular fisheye distortion, and 's'
results in a planisphere (stereographic) projection.
A hemispherical fisheye is a projection of the hemisphere onto a circle.
The maximum view angle for this type is 180 degrees.
An angular fisheye view is defined such that distance from the center of
the image is proportional to the angle from the central view direction.
An angular fisheye can display a full 360 degrees.
A planisphere fisheye view maintains angular relationships between lines,
and is commonly used for sun path analysis.
This is more commonly known as a
"stereographic projection," but we avoid the term here so as not to
confuse it with a stereoscopic pair.
A planisphere fisheye can display up to (but not including) 360 degrees,
although distortion becomes extreme as this limit is approached.
Note that there is no space between the view type
option and its single letter argument.
.TP
.BI -vp " x y z"
Set the view point to
.I "x y z".
This is the focal point of a perspective view or the
center of a parallel projection.
.TP
.BI -vd " xd yd zd"
Set the view direction vector to
.I "xd yd zd".
The length of this vector indicates the focal distance as needed by the
.I \-pd
option, described below.
.TP
.BI -vu " xd yd zd"
Set the view up vector (vertical direction) to
.I "xd yd zd".
.TP
.BI -vh \ val
Set the view horizontal size to
.I val.
For a perspective projection (including fisheye views),
.I val
is the horizontal field of view (in degrees).
For a parallel projection,
.I val
is the view width in world coordinates.
.TP
.BI -vv \ val
Set the view vertical size to
.I val.
.TP
.BI -vo \ val
Set the view fore clipping plane at a distance of
.I val
from the view point.
The plane will be perpendicular to the view direction for
perspective and parallel view types.
For fisheye view types, the clipping plane is actually a clipping
sphere, centered on the view point with radius
.I val.
Objects in front of this imaginary surface will not be visible.
This may be useful for seeing through walls (to get a longer
perspective from an exterior view point) or for incremental
rendering.
A value of zero implies no foreground clipping.
A negative value produces some interesting effects, since it creates an
inverted image for objects behind the viewpoint.
This possibility is provided mostly for the purpose of rendering
stereographic holograms.
.TP
.BI -va \ val
Set the view aft clipping plane at a distance of
.I val
from the view point.
Like the view fore plane, it will be perpendicular to the view
direction for perspective and parallel view types.
For fisheye view types, the clipping plane is actually a clipping
sphere, centered on the view point with radius
.I val.
Objects behind this imaginary surface will not be visible.
A value of zero means no aft clipping, and is the only way to see
infinitely distant objects such as the sky.
.TP
.BI -vs \ val
Set the view shift to
.I val.
This is the amount the actual image will be shifted to the right of
the specified view.
This is option is useful for generating skewed perspectives or
rendering an image a piece at a time.
A value of 1 means that the rendered image starts just to the right of
the normal view.
A value of \-1 would be to the left.
Larger or fractional values are permitted as well.
.TP
.BI -vl \ val
Set the view lift to
.I val.
This is the amount the actual image will be lifted up from the
specified view, similar to the
.I \-vs
option.
.TP
.BI -vf \ file
Get view parameters from
.I file,
which may be a picture or a file created by rvu (with the "view" command).
.TP
.BI -x \ res
Set the maximum x resolution to
.I res.
.TP
.BI -y \ res
Set the maximum y resolution to
.I res.
.TP
.BI -pa \ rat
Set the pixel aspect ratio (height over width) to
.I rat.
Either the x or the y resolution will be reduced so that the pixels have
this ratio for the specified view.
If
.I rat
is zero, then the x and y resolutions will adhere to the given maxima.
.TP
.BI -ps \ size
Set the pixel sample spacing to the integer
.I size.
This specifies the sample spacing (in pixels) for adaptive subdivision
on the image plane.
.TP
.BI -pt \ frac
Set the pixel sample tolerance to
.I frac.
If two samples differ by more than this amount, a third
sample is taken between them.
.TP
.BI -pj \ frac
Set the pixel sample jitter to
.I frac.
Distributed ray-tracing performs anti-aliasing by randomly sampling
over pixels.
A value of one will randomly distribute samples over full
pixels.
A value of zero samples pixel centers only.
A value between zero and one is usually best
for low-resolution images.
.TP
.BI -pm \ frac
Set the pixel motion blur to
.I frac.
In an animated sequence, the exact view will be blurred between the previous
view and the next view as though a shutter were open this fraction of a
frame time.
(See the
.I \-S
option regarding animated sequences.)\0
The first view will be blurred according to the difference between the
initial view set on the command line and the first view taken from the
standard input.
It is not advisable to use this option in combination with the
.I pmblur(1)
program, since one takes the place of the other.
However, it may improve results with
.I pmblur
to use a very small fraction with the
.I \-pm
option, to avoid the ghosting effect of too few time samples.
.TP
.BI -pd \ dia
Set the pixel depth-of-field aperture to a diameter of
.I dia
(in world coordinates).
This will be used in conjunction with the view focal distance, indicated
by the length of the view direction vector given in the
.I \-vd
option.
It is not advisable to use this option in combination with the
.I pdfblur(1)
program, since one takes the place of the other.
However, it may improve results with
.I pdfblur
to use a very small fraction with the
.I \-pd
option, to avoid the ghosting effect of too few samples.
.TP
.BI -dj \ frac
Set the direct jittering to
.I frac.
A value of zero samples each source at specific sample points
(see the
.I \-ds
option below), giving a smoother but somewhat less accurate
rendering.
A positive value causes rays to be distributed over each
source sample according to its size, resulting in more accurate
penumbras.
This option should never be greater than 1, and may even
cause problems (such as speckle) when the value is smaller.
A warning about aiming failure will issued if
.I frac
is too large.
It is usually wise to turn off image sampling when using
direct jitter by setting \-ps to 1.
.TP
.BI -ds \ frac
Set the direct sampling ratio to
.I frac.
A light source will be subdivided until
the width of each sample area divided by the distance
to the illuminated point is below this ratio.
This assures accuracy in regions close to large area sources
at a slight computational expense.
A value of zero turns source subdivision off, sending at most one
shadow ray to each light source.
.TP
.BI -dt \ frac
Set the direct threshold to
.I frac.
Shadow testing will stop when the potential contribution of at least
the next and at most all remaining light source samples is less than
this fraction of the accumulated value.
(See the
.I \-dc
option below.)\0
The remaining light source contributions are approximated
statistically.
A value of zero means that all light source samples will be tested for shadow.
.TP
.BI \-dc \ frac
Set the direct certainty to
.I frac.
A value of one guarantees that the absolute accuracy of the direct calculation
will be equal to or better than that given in the
.I \-dt
specification.
A value of zero only insures that all shadow lines resulting in a contrast
change greater than the
.I \-dt
specification will be calculated.
.TP
.BI -dr \ N
Set the number of relays for secondary sources to
.I N.
A value of 0 means that secondary sources will be ignored.
A value of 1 means that sources will be made into first generation
secondary sources; a value of 2 means that first generation
secondary sources will also be made into second generation secondary
sources, and so on.
.TP
.BI -dp \ D
Set the secondary source presampling density to D.
This is the number of samples per steradian 
that will be used to determine ahead of time whether or not
it is worth following shadow rays through all the reflections and/or
transmissions associated with a secondary source path.
A value of 0 means that the full secondary source path will always
be tested for shadows if it is tested at all.
.TP
.BR \-dv
Boolean switch for light source visibility.
With this switch off, sources will be black when viewed directly
although they will still participate in the direct calculation.
This option may be desirable in conjunction with the
.I \-i
option so that light sources do not appear in the output.
.TP
.BI -ss \ samp
Set the specular sampling to
.I samp.
For values less than 1, this is the degree to which the highlights
are sampled for rough specular materials.
A value greater than one causes multiple ray samples to be sent
to reduce noise at a commmesurate cost.
A value of zero means that no jittering will take place, and all
reflections will appear sharp even when they should be diffuse.
This may be desirable when used in combination with image sampling
(see
.I \-ps
option above) to obtain faster renderings.
.TP
.BI -st \ frac
Set the specular sampling threshold to
.I frac.
This is the minimum fraction of reflection or transmission, under which 
no specular sampling is performed.
A value of zero means that highlights will always be sampled by
tracing reflected or transmitted rays.
A value of one means that specular sampling is never used.
Highlights from light sources will always be correct, but
reflections from other surfaces will be approximated using an
ambient value.
A sampling threshold between zero and one offers a compromise between image
accuracy and rendering time.
.TP
.BR -bv
Boolean switch for back face visibility.
With this switch off, back faces of all objects will be invisible
to view rays.
This is dangerous unless the model was constructed such that
all surface normals face outward.
Although turning off back face visibility does not save much
computation time under most circumstances, it may be useful as a
tool for scene debugging, or for seeing through one-sided walls from
the outside.
.TP
.BI -av " red grn blu"
Set the ambient value to a radiance of
.I "red grn blu".
This is the final value used in place of an
indirect light calculation.
If the number of ambient bounces is one or greater and the ambient
value weight is non-zero (see
.I -aw
and
.I -ab
below), this value may be modified by the computed indirect values
to improve overall accuracy.
.TP
.BI -aw \ N
Set the relative weight of the ambient value given with the
.I -av
option to
.I N.
As new indirect irradiances are computed, they will modify the
default ambient value in a moving average, with the specified weight
assigned to the initial value given on the command and all other
weights set to 1.
If a value of 0 is given with this option, then the initial ambient
value is never modified.
This is the safest value for scenes with large differences in
indirect contributions, such as when both indoor and outdoor
(daylight) areas are visible.
.TP
.BI -ab \ N
Set the number of ambient bounces to
.I N.
This is the maximum number of diffuse bounces computed by the indirect
calculation. A value of zero implies no indirect calculation. 
.IP
This value defaults to 1 in photon mapping mode (see
.I -ap
below), implying that global photon irradiance is always computed via
.I one
ambient bounce; this behaviour applies to any positive number of ambient
bounces, regardless of the actual value specified.  A negative value enables
a preview mode that directly visualises the irradiance from the global
photon map without any ambient bounces.
.TP
.BI -ar \ res
Set the ambient resolution to
.I res.
This number will determine the maximum density of ambient values
used in interpolation.
Error will start to increase on surfaces spaced closer than
the scene size divided by the ambient resolution.
The maximum ambient value density is the scene size times the
ambient accuracy (see the
.I \-aa
option below) divided by the ambient resolution.
The scene size can be determined using
.I getinfo(1)
with the
.I \-d
option on the input octree.
A value of zero is interpreted as unlimited resolution.
.TP
.BI -aa \ acc
Set the ambient accuracy to
.I acc.
This value will approximately equal the error
from indirect illuminance interpolation.
A value of zero implies no interpolation.
.TP
.BI -ad \ N
Set the number of ambient divisions to
.I N.
The error in the Monte Carlo calculation of indirect
illuminance will be inversely proportional to the square
root of this number.
A value of zero implies no indirect calculation.
.TP
.BI -as \ N
Set the number of ambient super-samples to
.I N.
Super-samples are applied only to the ambient divisions which
show a significant change.
.TP
.BI -af \ fname
Set the ambient file to
.I fname.
This is where indirect illuminance will be stored and retrieved.
Normally, indirect illuminance values are kept in memory and
lost when the program finishes or dies.
By using a file, different invocations can share illuminance
values, saving time in the computation.
Also, by creating an ambient file during a low resolution rendering,
better results can be obtained in a second high resolution pass.
The ambient file is in a machine-independent binary format
which may be examined with
.I lookamb(1).
.IP
The ambient file may also be used as a means of communication and
data sharing between simultaneously executing processes.
The same file may be used by multiple processes, possibly running on
different machines and accessing the file via the network (ie.
.I nfs(4)).
The network lock manager
.I lockd(8)
is used to insure that this information is used consistently.
.IP
If any calculation parameters are changed or the scene
is modified, the old ambient file should be removed so that
the calculation can start over from scratch.
For convenience, the original ambient parameters are listed in the
header of the ambient file.
.I Getinfo(1)
may be used to print out this information.
.TP
.BI -ae \ mod
Append
.I mod
to the ambient exclude list,
so that it will not be considered during the indirect calculation.
This is a hack for speeding the indirect computation by
ignoring certain objects.
Any object having
.I mod
as its modifier will get the default ambient
level rather than a calculated value.
Any number of excluded modifiers may be given, but each
must appear in a separate option.
.TP
.BI -ai \ mod
Add
.I mod
to the ambient include list,
so that it will be considered during the indirect calculation.
The program can use either an include list or an exclude
list, but not both.
.TP
.BI -aE \ file
Same as
.I \-ae,
except read modifiers to be excluded from
.I file.
The RAYPATH environment variable determines which directories are
searched for this file.
The modifier names are separated by white space in the file.
.TP
.BI -aI \ file
Same as
.I \-ai,
except read modifiers to be included from
.I file.
.TP
.BI -ap " file [bwidth1 [bwidth2]]"
Enable photon mapping mode. Loads a photon map generated with
.I mkpmap(1)
from
.I file,
and evaluates the indirect irradiance depending on the photon type 
(automagically detected) using density estimates with a bandwidth of
.I bwidth1
photons, or the default bandwidth if none is specified (a warning will be
issued in this case).
.IP
Global photon irradiance is evaluated as part of the ambient calculation (see
.I \-ab
above), caustic photon irradiance is evaluated at primary rays, and 
indirect inscattering in 
.I mist
is accounted for by volume photons. Contribution photons are treated as
global photons by
.I rpict.
.IP
Additionally specifying 
.I bwidth2
enables bias compensation for the density estimates with a
minimum and maximum bandwidth of
.I bwidth1
and
.I bwidth2,
respectively.
.IP
Global photon irradiance may be optionally precomputed by
.I mkpmap(1),
in which case the bandwidth, if specified, is ignored, as the nearest photon
is invariably looked up.
.IP
Using direct photons replaces the direct calculation with density estimates
for debugging and validation of photon emission.
.TP
.BI -am " frac"
Maximum search radius for photon map lookups.  Without this option, an
initial maximum search radius is estimated for each photon map from the
average photon distance to the distribution's centre of gravity.  It is then
adapted to the photon density in subsequent lookups.  This option imposes a
global fixed maximum search radius for
.I all
photon maps, thus defeating the automatic adaptation.  It is useful when
multiple warnings about short photon lookups are issued.  Note that this
option does not conflict with the bandwidth specified with the
.I \-ap
option; the number of photons found will not exceed the latter, but may be
lower if the maximum search radius contains fewer photons, thus resulting in
short lookups.  Setting this radius too large, on the other hand, may
degrade performance.
.TP
.BI -ac " pagesize"
Set the photon cache page size when using out-of-core photon mapping. The
photon cache reduces disk I/O incurred by on-demand loading (paging) of
photons, and thus increases performance. This
is expressed as a (float) multiple of the density estimate bandwidth
specified with
.I \-ap
under the assumption that photon lookups are local to a cache page. Cache
performance is sensitive to this parameter: larger pagesizes will reduce the
paging frequency at the expense of higher latency when paging does occur.
Sensible values are in the range 4 (default) to 16.
.TP
.BI -aC " cachesize"
Set the total number of photons cached when using out-of-core photon
mapping, taking into account the pagesize specified by
.I \-ac. 
Note that this is approximate as the number of cache pages is rounded to
the nearest prime. This allows adapting the cache to the available physical
memory. In conjunction with the
.I \-n
option, this is the cache size
.I per parallel process. 
Cache performance is less sensitive to this parameter,
and reasonable performance can obtained with as few as 10k photons. The
default is 1M. This option recognises multiplier suffixes (k = 1e3, M =
1e6), both in upper and lower case.
.TP
.BI -me " rext gext bext"
Set the global medium extinction coefficient to the indicated color,
in units of 1/distance (distance in world coordinates).
Light will be scattered or absorbed over distance according to
this value.
The ratio of scattering to total scattering plus absorption is set
by the albedo parameter, described below.
.TP
.BI -ma " ralb galb balb"
Set the global medium albedo to the given value between 0\00\00
and 1\01\01.
A zero value means that all light not transmitted by the medium
is absorbed.
A unitary value means that all light not transmitted by the medium
is scattered in some new direction.
The isotropy of scattering is determined by the Heyney-Greenstein
parameter, described below.
.TP
.BI \-mg \ gecc
Set the medium Heyney-Greenstein eccentricity parameter to
.I gecc.
This parameter determines how strongly scattering favors the forward
direction.
A value of 0 indicates perfectly isotropic scattering.
As this parameter approaches 1, scattering tends to prefer the
forward direction.
.TP
.BI \-ms \ sampdist
Set the medium sampling distance to
.I sampdist,
in world coordinate units.
During source scattering, this will be the average distance between
adjacent samples.
A value of 0 means that only one sample will be taken per light
source within a given scattering volume.
.TP
.BR \-i
Boolean switch to compute irradiance rather than radiance values.
This only affects the final result, substituting a Lambertian
surface and multiplying the radiance by pi.
Glass and other transparent surfaces are ignored during this stage.
Light sources still appear with their original radiance values,
though the
.I \-dv
option (above) may be used to override this.
.TP
.BR \-u
Boolean switch to control uncorrelated random sampling.
When "off", a low-discrepancy sequence is used, which reduces
variance but can result in a dithered appearance in specular highlights.
When "on", pure Monte Carlo sampling is used in all calculations.
.TP
.BI -lr \ N
Limit reflections to a maximum of
.I N,
if N is a positive integer.
If
.I N
is zero, then Russian roulette is used for ray
termination, and the
.I -lw
setting (below) must be positive.
If N is a negative integer, then this sets the upper limit
of reflections past which Russian roulette will be used.
In scenes with dielectrics and total internal reflection,
a setting of 0 (no limit) may cause a stack overflow.
.TP
.BI -lw \ frac
Limit the weight of each ray to a minimum of
.I frac.
During ray-tracing, a record is kept of the estimated contribution
(weight) a ray would have in the image.
If this weight is less than the specified minimum and the
.I -lr
setting (above) is positive, the ray is not traced.
Otherwise, Russian roulette is used to
continue rays with a probability equal to the ray weight
divided by the given
.I frac.
.TP
.BI -S \ seqstart
Instead of generating a single picture based only on the view
parameters given on the command line, this option causes
.I rpict
to read view options from the standard input and for each line
containing a valid view specification, generate a corresponding
picture.
This option is most useful for generating animated sequences, though
it may also be used to control rpict from a remote process for
network-distributed rendering.
.I Seqstart
is a positive integer that will be associated with the first output
frame, and incremented for successive output frames.
By default, each frame is concatenated to the output stream, but it
is possible to change this action using the
.I \-o
option (described below).
Multiple frames may be later extracted from the output using
.I ra_rgbe(1).
.IP
Note that the octree may not be read from the standard input when
using this option.
.TP
.BI -o \ fspec
Send the picture(s) to the file(s) given by
.I fspec
instead of the standard output.
If this option is used in combination with
.I \-S
and
.I fspec
contains an integer field for
.I printf(3)
(eg. "%03d") then the actual output file name will include
the current frame number.
.I Rpict
will not allow a picture file to be clobbered (overwritten)
with this option.
If an image in a sequence already exists
.I (\-S
option),
.I rpict
will skip until it reaches an image that doesn't, or the end of
the sequence.
This is useful for running rpict on multiple machines or processors
to render the same sequence, as each process will skip to the next
frame that needs rendering.
.TP
.BI -r \ fn
Recover pixel information from the file
.I fn.
If the program gets killed during picture generation, the information
may be recovered using this option.
The view parameters and picture dimensions are also recovered from
.I fn
if possible.
The other options should be identical to those which created
.I fn,
or an inconsistent picture may result.
If
.I fn
is identical to the file specification given with the
.I \-o
option,
.I rpict
will rename the file prior to copying its contents.
This insures that the old file is not overwritten accidentally.
(See also the
.I \-ro
option, below.)\0
.IP
If 
.I fn
is an integer and the recover option is used in combination with the
.I \-S
option, then
.I rpict
skips a number of view specifications on its input equal to the
difference between
.I fn
and
.I seqstart.
.I Rpict
then performs a recovery operation on the file constructed from the
frame number
.I fn
and the output file specification given with the
.I \-o
option.
This provides a convenient mechanism for recovering in the middle of
an aborted picture sequence.
.IP
The recovered file
will be removed if the operation is successful.
If the recover operation fails (due to lack of disk space)
and the output file and recover file specifications
are the same, then the original information may be left in a
renamed temporary file.
(See FILES section, below.)\0
.TP
.BI -ro \ fspec
This option causes pixel information to be recovered from and
subsequently returned to the picture file
.I fspec.
The effect is the same as specifying identical recover and output
file names with the
.I \-r
and
.I \-o
options.
.TP
.BI -z \ fspec
Write pixel distances out to the file
.I fspec.
The values are written as short floats, one per pixel in scanline order,
as required by
.I pinterp(1).
Similar to the
.I \-o
option, the actual file name will be constructed using
.I printf
and the frame number from the
.I \-S
option.
If used with the
.I \-r
option, 
.I \-z
also recovers information from an aborted rendering.
.TP
.BI \-P \ pfile
Execute in a persistent mode, using
.I pfile
as the control file.
This option must be used together with
.I \-S,
and is incompatible with the recover option
.I (\-r).
Persistent execution means that after reaching end-of-file on
its input,
.I rpict
will fork a child process that will wait for another
.I rpict
command with the same
.I \-P
option to attach to it.
(Note that since the rest of the command line options will be those
of the original invocation, it is not necessary to give any arguments
besides
.I \-P
for subsequent calls.)
Killing the process is achieved with the
.I kill(1)
command.
(The process ID in the first line of
.I pfile
may be used to identify the waiting
.I rpict
process.)
This option may be less useful than the
.I \-PP
variation, explained below.
.TP
.BI \-PP \ pfile
Execute in continuous-forking persistent mode, using
.I pfile
as the control file.
The difference between this option and the
.I \-P
option described above is the creation of multiple duplicate
processes to handle any number of attaches.
This provides a simple and reliable mechanism of memory sharing
on most multiprocessing platforms, since the
.I fork(2)
system call will share memory on a copy-on-write basis.
This option may be used with
.I rpiece(1)
to efficiently render a single image using multiple processors
on the same host.
.TP
.BI -t \ sec
Set the time between progress reports to
.I sec.
A progress report writes the number of rays traced, the percentage
completed, and the CPU usage to the standard error.
Reports are given either automatically after the specified interval,
or when the process receives a continue (\-CONT) signal (see
.I kill(1)).
A value of zero turns automatic reporting off.
.TP
.BI -e \ efile
Send error messages and progress reports to
.I efile
instead of the standard error.
.TP
.BR \-w
Boolean switch for warning messages.
The default is to print warnings, so the first appearance of
this option turns them off.
.SH EXAMPLE
rpict \-vp 10 5 3 \-vd 1 \-.5 0 scene.oct > scene.hdr
.PP
rpict \-S 1 \-o frame%02d.hdr scene.oct < keyframes.vf
.PP
To render ambient illuminance in photon mapping mode from a global photon 
map global.pm via one ambient bounce, and from a caustic photon map 
caustic.pm:
.IP "" .2i
rpict -ab 1 -ap global.pm 50 -ap caustic.pm 50 -vf scene.vf scene.oct > 
scene.hdr
.SH ENVIRONMENT
RAYPATH		the directories to check for auxiliary files.
.SH FILES
/tmp/rtXXXXXX		common header information for picture sequence
.br
rfXXXXXX		temporary name for recover file
.SH DIAGNOSTICS
If the program terminates from an input related error, the exit status
will be 1.
A system related error results in an exit status of 2.
If the program receives a signal that is caught, it will exit with a status
of 3.
In each case, an error message will be printed to the standard error, or
to the file designated by the
.I \-e
option.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
getinfo(1), lookamb(1), mkpmap(1), oconv(1), pdfblur(1), pfilt(1), 
pinterp(1), pmblur(1), printf(3), ra_rgbe(1), rad(1), rpiece(1), rtpict(1), rtrace(1), rvu(1)
